This application claims the priority of German Application No. 199 20 096.3, filed May 3, 1999, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a device for controlling brake lights in a vehicle with a brake system designed for outside force actuation. A control unit controls the vehicle brakes and a brake light switch located in the vicinity of a brake pedal. The switch is connected with a control device to control at least one brake light.
In motor vehicles, brake light switches are usually installed in the vicinity of the brake pedal and are activated when a brake pedal is operated. The brake light switch then operates the brake lights directly or through a control device located in between, to indicate to following traffic that a leading vehicle is being braked.
The use of brake-regulating systems poses problems in this regard, especially use of vehicle speed-regulating systems that perform active braking intervention without a brake pedal being operated by a vehicle owner. Without suitable measures, the brake light cannot be controlled during such braking intervention. Consequently, the application of the brake is not indicated to following traffic.
To avoid this problem, a system is known which operates the brake pedal itself during a braking intervention. In this known system, in the event of a brake application by a vehicle spacing regulating device, a vacuum braking force amplifier is controlled electrically. This then pulls the brake pedal forward so that the conventional brake light switch is actuated in its normal fashion.
This procedure however means that in the event of a braking intervention by the driver, the brake pedal is not in its usual position. This may require some getting used to and may irritate the driver.
In addition to the system described above in which the brake pedal is pulled forward, an application is also possible in which, during an active braking intervention, especially a spacing regulating intervention, an active braking regulating system is operated by a hydraulic assembly without the brake pedal moving. The brake light switch is not actuated, however.
The goal of the present invention is to provide a device which avoids this disadvantage. In particular, a brake light must be controlled so that it appears plausible to following traffic.
This goal is achieved by a device for brake light control in a vehicle with a brake system designed for outside force actuation. A control unit controls the vehicle brakes and a brake light switch located in the vicinity of a brake pedal. The switch is connected with a control device to control at least one brake light. The control unit is coupled with the control device and operates the latter so that the at least one brake light, even without operation of the brake light switch, can be activated under first defined vehicle operation conditions and is deactivatable under second defined vehicle operating conditions.
In particular, a control unit that serves to control vehicle brakes is connected with a control device that serves to control the brake lights. The control device is actuated by the control unit so that the brake lights can be activated even without operating the brake light switch under first defined vehicle operating conditions and can be deactivated under second defined vehicle operating conditions.
In the brake system, a conventional hydraulic system with a hydraulic assembly may be used. The hydraulic system is actuated by the control unit for regulating the braking pressures on the individual vehicle brakes. Of course, the present invention can also be used on all other brake systems actuated by outside forces. Thus, the brake system can be equipped with electromechanical vehicle brakes that are actuated directly and individually by a suitably designed control unit. The operating conditions must be chosen so that a brake application displayed to following traffic appears plausible.
According to a preferred embodiment of the invention, conditions are specified as criteria in which, for example, an active pressure increase by the hydraulic assembly takes place. This means that the hydraulic assembly is activated for a controlling brake application. In addition, the vehicle actual deceleration must exceed a certain threshold value, in other words deceleration must be present to a sufficient extent. Further, the hydraulic pressure developed in the hydraulic assembly must be higher than a certain threshold value, 2 bars for example.
Deactivation of the brake lights can be undertaken when: (1) the pressure development by the hydraulic assembly is terminated, (2) the vehicle actual deceleration falls below a certain threshold, in other words the deceleration is below a certain boundary deceleration, or (3) the hydraulic pressure in the brake system falls below a certain value. The two boundary deceleration values for activation of the brake light and for deactivation of the brake light can differ by an offset so that a control hysteresis is formed that avoids a tendency of the brake light to flicker.
According to another preferred embodiment of the invention, a device for determining the vehicle""s actual deceleration is provided. A corresponding vehicle actual deceleration value is provided to the control unit so that one of the above criteria can be checked. In a simple embodiment, at least one wheel rpm sensor is provided to determine the actual deceleration of the vehicle.
It is also logical to provide a device for determining the hydraulic pressure in a hydraulic brake system between the hydraulic assembly and the wheel brakes so that the criterion of exceeding a pressure threshold value can be checked. According to a first embodiment, this device can be provided in the form of a calculating unit which estimates the hydraulic pressure, for example from the control times of valves installed in the hydraulic assemblies and a feedback pump. The estimate is generally conducted according to a certain model.
If pressure sensors are located between the hydraulic assembly and the wheel brakes, the hydraulic pressure can also be detected directly as an alternative.
To consider the grade of the road, the first vehicle deceleration boundary value increases with the brake lights being activated as a criterion, preferably with increasing hydraulic pressure. In particular, this increase is linear. In a graph representing hydraulic pressure as a function of actual deceleration, the first vehicle deceleration boundary value intersects the ordinate, in other words the axis for actual deceleration at a specified pressure of 0 bar at a value that is composed of a speed-dependent deceleration and a fixed offset value. The abscissa is intersected at one point by the vehicle deceleration boundary value at a deceleration of 0 m/sec2 at which a downhill driving force compensates for a certain slope. A slope of 10% is assumed to be the slope for example. The reason for this will be explained later.